User manual

78
Figure 2: Collimator star shot
C. Couch Star Shot
1. Tape a sheet of film at the center of one of the plastic slabs with the edges
of the film and the slab roughly parallel to one another.
2. Place the slab under the head of the linac with the film on top and the long
edge of the film roughly parallel to the longitudinal axis and the center of
the film roughly at isocenter.
3. Using the laser lines and light field markers adjust the couch height and
slab/film position so the film is level and at isocenter. Using a fine-tipped
marker scribe marks near the edges of the film to indicate the position of
the longitudinal and transverse crosshairs.
4. Close the collimator to produce a slit beam about 2-4 mm wide and
parallel to the longitudinal axis. Note: The beam width will influence the